In order to stabilize supersonic combustion using a fuel of hydrocarbon system, it is desirable to increase a rate of hydrocarbon with small carbon number in a fuel, and keep a distribution of the carbon number constant in the fuel. Also, since the hydrocarbon with small carbon number is a gas state at normal temperature, when the hydrocarbon with small carbon number is mounted on a fuel tank, Fuel on Board cannot be increased and supersonic combustion (supersonic flight) cannot be realized for long periods of time. Therefore, it is considered to mount hydrocarbon with large carbon number as a main component, which is liquid at normal temperature, on the fuel tank, and decompose the liquid hydrocarbon fuel by heat of an engine during a flight for obtaining a reformed fuel that includes hydrocarbon with small carbon number as a main component.
Patent literature 1 discloses a heat management system of a propulsion engine for a supersonic and hypersonic aircraft. The system uses a single flow of endothermic fluid as a fuel and a heatsink for cooling the engine. The system includes a plurality of heat exchanger arranged in series. Each heat exchanger includes a reaction section having a catalyst so as to exchange heat with a heat source section. The single flow of fluid flows through each of the reaction section and the heat source section. Heat for a reaction in the reaction section is given from fluid in the heat source section, and thereby the fluid is cooled. This cooled fluid is heated again when flowing through a hot section of the engine, and flows toward other reaction section or flows toward a combustor of the engine to be fired.
Patent literature 2 discloses a method of enhancing combustion speed to expand a limit of an accidental fire in a high-speed propulsion unit such as a ramjet and scramjet engine. A flow of a hydrocarbon system fuel is decomposed by a catalyst to generate hydrogen and a fuel resolvent of low-molecular weight. The hydrogen and the fuel resolvent of low-molecular weight are introduced into a combustor of the high-speed propulsion unit with a flow of the hydrocarbon system fuel which is not decomposed. According to this method, an operation range of the combustor expands, and a high combustion speed and an enhancement of flame stability are achieved by higher-speed diffusive mixing. This process effectively expands an operation limit of a gas turbine, especially of a ramjet and scramjet combustor.
Moreover, patent literature 2 discloses followings. The fuel is vaporized in a catalytic reaction section to be decomposed by catalysts into hydrogen and fuel resolvent of low-molecular weight. What type of fuel is generated depends on what type of fuel is introduced into the reaction section. Preferable catalysts used in the reaction section include platinum group metals such as platinum, rhodium, iridium, and palladium. It is indicated that catalysts including other metals such as nickel, chromium, and cobalt are also effective. The catalysts may be composed by a single metal, and may be composed by a combination of appropriate metals.
In a catalytic reaction, there is an effective temperature range for respective catalysts, and the catalytic reaction should be managed in this range. However, since a temperature of a combustion chamber of the scramjet engine is very high and is equal to or more than thousands degrees C., it is very difficult to control a temperature of the catalyst arranged near the combustion chamber to be a desired temperature by using a heat generated by the combustion chamber. When the heat supplied to a catalytic layer is excessive, there is a possibility that the temperature of the catalyst becomes too high, the catalyst is inactivated, heat decomposition becomes difficult, and generation of the reformed fuel becomes difficult. Furthermore, when a temperature of a catalytic reaction region is unstable, there is a possibility that fuels of liquid state and gas state are mixed, the catalyst is stripped from a flow channel by vaporization/bumping of fuels to block the flow channel, and supply of the reformed fuel becomes difficult.